Does DLVRD support HEVC, 10-bit and HDR playback?

Yes. You can upload HEVC and 10-bit masters to DLVRD, and the file your client downloads is that original, untouched. For in-gallery streaming, DLVRD generates H.264 playback renditions by default for maximum compatibility, with HEVC 10-bit streaming available as an option for higher-fidelity playback on devices that support it.

The reasoning is practical. H.264 8-bit plays on effectively every browser and device on earth, which is what you want for a client opening the link on an unknown phone. HEVC 10-bit preserves more gradation in skies, skin tones and graded footage, but not every device decodes it in the browser. Offering both gives you compatibility by default and fidelity when you choose it.

Whatever the streaming settings, quality-critical viewing should happen on the downloaded master, and that is always the exact file you exported.